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      <title>分布式系统中的负载均衡策略 - 交互式测验</title>
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        #question-text {
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          font-weight: 500;
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        .options-list {
          list-style: none;
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        .option-item {
          background-color: #f8f9fa;
          border: 1px solid #dee2e6;
          border-radius: 8px;
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          margin-bottom: 12px;
          cursor: pointer;
          transition: background-color 0.2s ease, border-color 0.2s ease;
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        .option-item:hover {
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        .option-item.selected {
            background-color: #d1e7fd;
            border-color: #4a90e2;
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        .quiz-footer {
          padding: 20px 30px;
          display: flex;
          justify-content: space-between; /* 将按钮分布在两侧 */
          align-items: center;
          min-height: 65px; /* Reserve space */
        }

        .nav-btn {
          background-color: #4a90e2;
          color: white;
          border: none;
          border-radius: 8px;
          padding: 10px 20px;
          font-size: 16px;
          font-weight: 500;
          cursor: pointer;
          transition: background-color 0.2s ease, transform 0.2s ease;
          box-shadow: 0 4px 12px rgba(0,0,0,0.15);
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        #next-btn {
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        .nav-btn:hover {
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        .result-box {
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        .source-text {
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            font-size: 14px;
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      </style>
    </head>
    <body>
      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>分布式系统中的负载均衡策略 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
                <div class="quiz-body">
                    <div class="progress-bar">
                        <div id="progress-indicator"></div>
                    </div>
                    <div id="question-container">
                      <p id="question-text"></p>
                      <ul class="options-list" id="options-list"></ul>
                    </div>
                    <div id="result-container"></div>
                    <div id="hint-container" class="hint-container"></div>
                </div>
                <div class="quiz-footer" id="quiz-footer">
                  <button id="prev-btn" class="nav-btn">上一题</button>
                  <button id="hint-btn" class="nav-btn" style="background-color: #ffc107; color: #333; box-shadow: 0 4px 12px rgba(255,193,7,0.3);">提示</button>
                  <button id="next-btn" class="nav-btn">下一题</button>
                </div>
            </div>
          </div>
      </div>

      <script>
        const quizData = [
  {
    "question": "根据文档，负载均衡的核心目标不包括以下哪一项？",
    "options": [
      "保障服务在部分实例故障时仍可用",
      "降低单个服务器的开发复杂度",
      "支持系统通过增减实例来应对流量变化",
      "提升系统整体性能和吞吐量"
    ],
    "correctAnswerIndex": 1,
    "explanation": "负载均衡的核心目标是优化整个系统的性能、可用性和可扩展性。它通过在多个服务器间分配流量来实现这一点，但它本身并不会降低单个服务器内部的业务逻辑开发复杂度。性能优化、高可用性和可扩展性是文档中明确列出的三大核心目标。",
    "source": "文档中「负载均衡的概述」->「核心目标」部分",
    "hint": "负载均衡旨在通过智能分发请求来优化系统整体的性能、可用性和可扩展性。"
  },
  {
    "question": "在分布式缓存场景中，当后端服务器发生增减变动时，与传统的哈希算法相比，一致性哈希算法有何主要优势？",
    "options": [
      "它能确保每个服务器的负载绝对均衡",
      "实现起来比传统哈希算法更简单",
      "只有一小部分请求会被重新分配，大多数缓存依然有效",
      "它完全不需要使用哈希函数来计算位置"
    ],
    "correctAnswerIndex": 2,
    "explanation": "传统哈希算法在服务器数量变动时，会导致大部分哈希映射失效，引发大规模缓存失效。而一致性哈希算法通过将服务器和请求都映射到哈希环上，当服务器变动时，只会影响环上的一小部分数据，从而最大限度地保留了现有缓存的有效性。",
    "source": "文档中「常见的负载均衡算法」->「7. 一致性哈希算法（Consistent Hashing）」部分",
    "hint": "传统哈希算法的一个缺点是当后端服务器变动时，可能引发大量的请求重新分配，这被称为“哈希失效问题”。"
  },
  {
    "question": "一个在线购物网站需要确保用户在添加商品到购物车后，后续的请求（如结算、修改数量）都能被路由到同一台服务器以维持会话状态。在这种场景下，哪种负载均衡策略最为适用？",
    "options": [
      "随机算法（Random）",
      "哈希算法（例如基于客户端IP）或会话保持（Sticky Sessions）",
      "最少连接算法（Least Connections）",
      "简单轮询算法（Round Robin）"
    ],
    "correctAnswerIndex": 1,
    "explanation": "有状态服务（如购物车）要求来自同一用户的连续请求被发送到同一台服务器。哈希算法（如IP Hash）和会话保持（Sticky Sessions）策略正是为此设计的，它们可以确保请求的“粘性”，从而维持会话的连续性。轮询、随机等算法无法保证这一点。",
    "source": "文档中「负载均衡策略的选择依据」->「3. 服务的业务特性」部分",
    "hint": "文档中提到，对于“有状态服务”，需要将来自同一用户的请求分配到同一个节点。"
  },
  {
    "question": "基于 DNS 的负载均衡实现方式简单，适合跨地域流量分发。但根据文档描述，它存在一个显著的缺点是什么？",
    "options": [
      "由于DNS缓存的存在，它无法实时感知后端服务器的健康状态",
      "它的配置过程非常复杂，需要专业网络知识",
      "成本远高于硬件负载均衡器",
      "只能处理HTTP协议的请求"
    ],
    "correctAnswerIndex": 0,
    "explanation": "DNS负载均衡的主要缺点在于其更新不及时。由于各级DNS服务器和客户端本地都可能存在缓存，当后端某台服务器发生故障时，DNS记录无法立即更新，导致在缓存过期前，仍有用户被解析到故障服务器的IP地址，从而影响服务的可用性。",
    "source": "文档中「负载均衡的实现方式」->「3. 基于 DNS 的负载均衡」部分",
    "hint": "考虑一下客户端或中间DNS服务器如何处理域名解析结果，这可能会导致延迟。"
  },
  {
    "question": "为了实现负载均衡的动态调整，系统需要实时监控后端服务的状态。以下哪项不是文档中提到的用于动态调整的关键性能指标？",
    "options": [
      "服务器的响应时间（Response Time）",
      "当前连接数（Connections）",
      "服务器的磁盘空间使用率",
      "节点的CPU和内存使用率（Resource Utilization）"
    ],
    "correctAnswerIndex": 2,
    "explanation": "动态调整依赖于能够实时反映服务器负载和健康状况的指标。文档明确列出了当前连接数、响应时间、CPU/内存使用率和错误率作为关键指标。而服务器的磁盘空间使用率通常不作为实时负载均衡决策的依据，因为它不直接反映当前请求处理能力。",
    "source": "文档中「负载均衡的动态调整」->「2. 动态调整的关键指标」部分",
    "hint": "动态调整的目标是根据服务的“实时负载”来分发请求，哪些指标最能反映实时负载？"
  },
  {
    "question": "文档对比了不同层级的负载均衡。与基于IP和端口进行流量分发的四层负载均衡（如LVS）相比，七层负载均衡（如Nginx）最主要的优势是什么？",
    "options": [
      "它的处理性能更高，延迟更低",
      "能够根据HTTP请求内容（如URL、头信息）进行更精细化的流量分发",
      "配置比四层负载均衡更简单"
    ],
    "correctAnswerIndex": 1,
    "explanation": "七层负载均衡工作在应用层，因此它可以解析HTTP等应用层协议的内容。这使得它能够实现更智能、更复杂的路由策略，例如根据不同的URL路径、请求头或Cookie将请求分发到不同的后端服务集群。而四层负载均衡仅在传输层工作，无法感知应用层数据。",
    "source": "文档中「负载均衡策略的选择依据」->「7. 网络协议层级」部分",
    "hint": "七层负载均衡工作在应用层，这意味着它可以“看懂”请求的具体内容。"
  },
  {
    "question": "假设一个服务器集群由多台性能不一的机器组成。为了让高性能服务器处理更多的请求，应优先选择哪种负载均衡算法？",
    "options": [
      "加权轮询（Weighted Round Robin）",
      "简单轮询（Round Robin）",
      "随机算法（Random）",
      "哈希算法（Hashing）"
    ],
    "correctAnswerIndex": 0,
    "explanation": "加权轮询算法是专门为处理性能不一致的服务器集群设计的。它允许为每台服务器设置一个权重值，负载均衡器会根据权重比例来分配请求，确保性能更高的服务器能接收到更多的流量，从而实现更合理的资源利用。",
    "source": "文档中「常见的负载均衡算法」->「2. 加权轮询（Weighted Round Robin）」部分",
    "hint": "文档中有一种算法明确提到了“根据服务器的性能设置权重，高性能服务器分配更多请求”。"
  }
];
        console.log("Quiz Data:", JSON.parse(JSON.stringify(quizData))); // 添加这行用于调试，以可展开的JSON格式输出
        
        let currentQuestionIndex = 0;
        let score = 0;
        // 存储每个问题的回答状态
        const userAnswers = new Array(quizData.length).fill(null); 

        const questionTextEl = document.getElementById('question-text');
        const optionsListEl = document.getElementById('options-list');
        const resultContainerEl = document.getElementById('result-container');
        const quizContentEl = document.getElementById('quiz-content');
        const progressIndicatorEl = document.getElementById('progress-indicator');
        const prevBtn = document.getElementById('prev-btn');
        const nextBtn = document.getElementById('next-btn');
        const hintBtn = document.getElementById('hint-btn');
        const hintContainerEl = document.getElementById('hint-container');

        function loadQuestion() {
          resultContainerEl.innerHTML = '';
          optionsListEl.innerHTML = '';
          hintContainerEl.style.display = 'none'; // 隐藏提示
          
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            return;
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          const currentQuestion = quizData[currentQuestionIndex];
          questionTextEl.textContent = `(${currentQuestionIndex + 1}/${quizData.length}) ${currentQuestion.question}`;
          
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            li.className = 'option-item';
            li.textContent = optionText;
            li.dataset.index = index; // Store index in a data attribute
            // 如果这道题已经回答过，恢复状态
            if (userAnswers[currentQuestionIndex] !== null) {
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                    li.classList.add('selected');
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            optionsListEl.appendChild(li);
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          // 如果已经回答过，直接显示结果
          if (userAnswers[currentQuestionIndex] !== null) {
              const isCorrect = userAnswers[currentQuestionIndex] === currentQuestion.correctAnswerIndex;
              showResult(isCorrect, currentQuestion);
          }
          
          updateNavigationButtons();
          updateProgress();
        }

        function selectOption(optionIndex) {
            userAnswers[currentQuestionIndex] = optionIndex;
            const currentQuestion = quizData[currentQuestionIndex];
            const isCorrect = optionIndex === currentQuestion.correctAnswerIndex;

            // 重新计算分数
            score = userAnswers.reduce((acc, answer, index) => {
                return answer === quizData[index].correctAnswerIndex ? acc + 1 : acc;
            }, 0);

            showResult(isCorrect, currentQuestion);
            updateNavigationButtons();
        }
        
        function updateProgress() {
            const answeredQuestions = userAnswers.filter(answer => answer !== null).length;
            const progressPercentage = (answeredQuestions / quizData.length) * 100;
            progressIndicatorEl.style.width = `${progressPercentage}%`;
        }
        
        function updateNavigationButtons() {
            prevBtn.style.display = 'block';
            nextBtn.style.display = 'block';
            hintBtn.style.display = 'block'; // 显示提示按钮

            prevBtn.disabled = currentQuestionIndex === 0;
            nextBtn.disabled = false; // 最后一题时，下一题按钮不禁用，而是用于显示报告
            nextBtn.textContent = (currentQuestionIndex === quizData.length - 1) ? '查看报告' : '下一题';
            
            // 如果当前问题没有提示，则禁用提示按钮并隐藏提示内容
            if (!quizData[currentQuestionIndex].hint) {
                hintBtn.disabled = true;
                hintContainerEl.style.display = 'none';
                hintContainerEl.textContent = ''; // 清除旧的提示内容
            } else {
                hintBtn.disabled = false;
            }
        }

        function showResult(isCorrect, questionData) {
            resultContainerEl.innerHTML = ''; // 清空之前的结果
            const resultBox = document.createElement('div');
            resultBox.className = `result-box ${isCorrect ? 'correct' : 'incorrect'}`;
            
            let html = `<h3>${isCorrect ? '回答正确！' : '回答错误'}</h3>`;
            if (!isCorrect) {
                html += `<p><strong>正确答案是：</strong> ${questionData.options[questionData.correctAnswerIndex]}</p>`;
            }
            html += `<div class="explanation-text">${questionData.explanation}</div>`;
            html += `<div class="source-text">来源: ${questionData.source}</div>`;
            
            resultBox.innerHTML = html;
            resultContainerEl.appendChild(resultBox);

            // 禁用所有选项的点击事件，并高亮正确/错误答案
            Array.from(optionsListEl.children).forEach((child, index) => {
                child.style.pointerEvents = 'none';
                // 高亮正确答案
                if (index === questionData.correctAnswerIndex) {
                    child.classList.add('correct'); // 需要添加CSS样式
                    child.style.backgroundColor = '#d4edda';
                    child.style.borderColor = '#c3e6cb';
                }
                // 如果选错了，高亮错误选项
                if (!isCorrect && index === userAnswers[currentQuestionIndex]) {
                    child.classList.add('incorrect'); // 需要添加CSS样式
                    child.style.backgroundColor = '#f8d7da';
                    child.style.borderColor = '#f5c6cb';
                }
            });
        }

        function goToNextQuestion() {
            if (currentQuestionIndex < quizData.length - 1) {
                currentQuestionIndex++;
                loadQuestion();
            } else {
                showFinalScore();
            }
        }

        function goToPreviousQuestion() {
            if (currentQuestionIndex > 0) {
                currentQuestionIndex--;
                loadQuestion();
            }
        }
        
        function showHint() {
            const currentQuestion = quizData[currentQuestionIndex];
            if (currentQuestion.hint) {
                hintContainerEl.textContent = currentQuestion.hint;
                hintContainerEl.style.display = 'block';
            } else {
                hintContainerEl.style.display = 'none';
            }
        }

        function showFinalScore() {
            document.querySelector('.quiz-body').style.display = 'none';
            document.getElementById('quiz-footer').style.display = 'none';

            const correctCount = score;
            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  